对表中数据分组,有时只需要某列的聚合值:有时却需要返回整行数据,常用的方法有:子查询.ROW_NUMBER.APPLY,总体感觉还是ROW_NUMBER比较直观.测试数据: if OBJECT_ID('testGroup') is not null drop table testGroup GO create table testGroup ( ID int identity primary key, UserID int, OrderID int ) GO insert testGroup ,
取SQL分组中的某几行数据 对表中数据分组,有时只需要某列的聚合值:有时却需要返回整行数据,常用的方法有:子查询.ROW_NUMBER.APPLY,总体感觉还是ROW_NUMBER比较直观.测试数据: if OBJECT_ID('testGroup') is not null drop table testGroup GO create table testGroup ( ID int identity primary key, UserID int, OrderID int ) GO inse
今天要做一个查询统计功能,一开始有点犯难,上午尝试大半天才写出统计sql语句,才发现自己sql分组查询及聚集函数没学好:其实就是group by子句和几个聚集函数,熟练使用统计功能很简单.在此总结下今天查询统计是用到的几个sql函数. SQL聚集函数 sum函数 sum函数用于计算查询表中指定字段中所有 记录值的总和. 语法:sum(exp) 说明:该函数不计算包含Null 值的字段. 例:SELECT SUM(population) FROM bbc 这里的SUM作用在所有返回记录的 popu
常用的方法有:子查询.ROW_NUMBER.APPLY,总体感觉还是ROW_NUMBER比较直观 if OBJECT_ID('testGroup') is not null drop table testGroup GO create table testGroup ( ID int identity primary key, UserID int, OrderID int ) GO insert testGroup , union all , union all , union all , u
I used to see my senior developers use WITH (NOLOCK) when querying in SQL Server and wonder why they use. Now i explored it and found that it's useful to improve the performance in executing the query . However there is a disadvantage in using it. Th
Ms Sql server 2005在开启Microsoft SQL Management时,如果出现"未能加载包“Microsoft SQL Management Studio Package”"这个错,则Microsoft SQL Management就会自动关闭,重新启动电脑也不能解决问题. 在网上搜索了下,在http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=349268&SiteID=1 处有解决办法,就是修复安
I used to see my senior developers use WITH (NOLOCK) when querying in SQL Server and wonder why they use. Now i explored it and found that it's useful to improve the performance in executing the query . However there is a disadvantage in using it. Th
把数据分成多个逻辑组,以便能对每个组的数据进行操作,对每个组进行聚集计算. 1.创建分组 分组是在SELECT语句的GROUP BY子句中建立的 例子: SELECT vendId,count(*) AS numProds FROM products GROUP BY vendId; GROUP BY子句指示分组数据,然后对每个组而不是整个数据集进行聚集. GROUP BY的一些注意事项: [1]在建立分组时,指定的所有列都一起计算,不能从个别列取回数据 [2]如果分组列中有
向mysql数据库中导入sql文件时,如果文件过大(几百M),会提示"Error Code: 1153 - Got a packet bigger than 'max_allowed_packet' bytes" 1.查看目前数据库配置 show VARIABLES like '%max_allowed_packet%'; 显示如下结果 +--------------------+---------+ | Variable_name | Value | +--------
